(1) Field of the Invention
The present invention relates to a camera-equipped wireless communications terminal, and in particular to a technique for suppressing interference.
(2) Description of the Related Art
Recently, mobile telephones, PDAs (Personal Digital Assistants), and the like which include imaging devices, referred to here as camera-equipped wireless communications terminals, have been widely embraced by consumers.
Camera-equipped wireless communications devices employing the communications method known as the FDD (Frequency Division Duplex) method split the frequency band that is to be used into transmission-use frequencies and a reception-use frequencies in order to realize simultaneous transmission and reception. However, in some instances the clock signal supplied to the camera module combines, as noise, with the transmission signal, causing the transmission frequency to approach to the reception frequency, and interference to occur in the reception circuit.
To be more specific about the cause of this phenomenon, the intermodulation product of the clock frequency supplying the camera module and the transmission frequency—the sum or difference of the transmission frequency and an nth harmonic (where n is a natural number) of the clock frequency—approaches a value close to the reception frequency, causing interference to occur. In order to avoid this, a method is conceivable by which the transmission frequency and the clock frequency are adjusted and set at the design stage such that the intermodulation product lies away from the reception frequency.
However, when a camera-equipped wireless communications terminal of the type that supports multiple bands communicates with a wireless base station through selective use of one of the plurality of FDD communication methods, each of which has a different gap between the transmission frequency band and the reception frequency band, the intermodulation product varies according to which FDD communications method is selected, and consequently, the method described above cannot be applied.